The expert phase of Coroner Alexander Ho’s inquest into the 3-year-old’s death continued in Invercargill today.
In 2019, Lachie was found 1.2km from his Gore home, face up in an oxidation pond.
Police quickly concluded the boy had drowned, but later confessed they "missed some steps" in the investigation.
Lachie’s father Paul Jones never believed his son drowned and suspected foul play.
Today, Karen Smith who worked for police in Florida for more than 13 years, including as a major crimes detective, says she had a "gift" for identifying overlooked details in cases.
Her opinion was that Lachie died earlier in the day and was placed into the oxidation pond to stage an accidental drowning.
She said Lachie’s mother Michelle Officer’s timeline was unable to be verified and there were many other gaps in the evidence.
Ms Smith alerted the court to "investigative red flags" which included failures by the police investigation, ambiguous witness statements and varying recollections of the night.
Robin Bates, counsel representing police, said Ms Smith had been biased in her findings.
"What your inquiry then has focused on is what happened in the course of the afternoon and in particular what Michelle did," Mr Bates said.
"You have gone looking as hard as you can trying to find a person who could [be responsible for Lachie’s death], and you've decided it was Michelle."
The witness denied this and said she was pointing out areas of the case that she thought needed to be further looked into.
